1. Field of the Invention
The invention relates to a switching power supply unit for converting an AC (Alternating Current) electric power into a DC (Direct Current) electric power and supplying it to a load and a disk array system and, more particularly, to a switching power supply unit having a backup function and a disk array system.
2. Description of the Related Art
Very high reliability is required for a power supply unit of a network information apparatus such as server, router, or disk array system. Not only at the time of maintenance and inspection but also at the time of an abnormality of a commercially available power supply such as power failure, instantaneous voltage drop (hereinafter, referred to as an “instantaneous drop”), or the like, even an instantaneous halt of the power supply unit is not permitted and uninterruption and non-short-break are indispensable. Ordinarily, the improvement of the reliability of the power supply is realized by adding a UPS (uninterruptible power supply unit). However, there is such a problem that since the UPS is connected between a commercially available power supply and a power supply in the information apparatus, the number of converters in a range from the commercially available power supply to the load increases, the realization of high efficiency is obstructed, and it is difficult to insert and pull out a hot line at the time of maintenance and inspection. Since volumes of a lead acid battery and an inverter circuit as component elements of the UPS are large, miniaturization of a power supply unit is also obstructed.
To solve the above problem, a power supply system construction in which a backup power supply is connected in parallel to a DC line in the power supply is used. The backup power supply is constructed by: a secondary battery having a high energy density such as nickel hydrogen battery, lithium ion battery, or the like; and its charging/discharging circuit. In a connecting position, a package form, a circuit system, and the like of the backup power supply, various kinds of techniques have been proposed. For example, there is a technique disclosed in JP-A-2004-7950. According to such a technique, a third winding (N3) is newly provided as a backup winding for a transformer in a switching power supply, and a secondary battery and a discharging switch are connected to the third winding (N3). At the time of a power failure, charges accumulated in a battery are discharged and a DC/DC converter is stably operated, thereby realizing electric power consumption for a load. A charging route to the battery is separately provided and a proper charging is performed from an output of a rectifying/smoothing circuit through a charging circuit. A charge/discharge control circuit for making charge/discharge control and the battery are built in a same casing as that of the switching power supply, thereby realizing miniaturization of a battery pack and high efficiency upon discharging. In addition, by properly managing the charge/discharge to/from the battery, a stable electric power supply to the load thereby is realized even at the time of the power failure. Further, by using such a structure that the discharging switch, charging circuit, charge/discharge control circuit, and the like are installed on a same circuit board together with the DC/DC converter and the rectifying/smoothing circuit and only the battery can be taken out of the casing of the switching power supply, ease of maintenance and inspection of the battery is improved.